An example of such composite door sensor is disclosed in a catalog of B.E.A. Inc., entitled “ACTIV8.3”, retrieved through the Internet at the B.E.A. Inc. website on Jan. 29, 2003.
The composite sensor disclosed in this catalog includes a microwave transmitter-receiver section and an infrared (IR) emitter-receiver section in a single casing. A microwave is used to detect a moving object, e.g. pedestrian, moving toward a door. When a pedestrian is detected by the microwave transmitter-receiver section, the door is opened. IR light is used to detect an object, e.g. a pedestrian, standing stationary in the vicinity of the door. When the pedestrian is detected by the IR emitter-receiver section, the door is kept open. The composite sensor is so arranged that an antenna for use in the microwave transmitter-receiver section can be adjusted in its angle with respect to the surface of the door within an angular range between 15 degrees and 50 degrees. The adjustment of the antenna angle can move the detection zone of the microwave transmitter-receiver section in the depth direction of the door, i.e. along the direction perpendicular to the door. In contrast, the detection zone of the IR emitter-receiver section cannot be moved in the depth direction of the door.
As described above, the microwave transmitter-receiver section is used to detect a moving pedestrian and activate the door. It may sometimes be desired to detect a pedestrian and activate the door to open when the pedestrian is at a relatively distant location from the door. For that purpose, the antenna may be installed with a large angle relative to the door surface so that the pedestrian can be detected at a location remote in the depth direction from the door. While the antenna angle can be set to such a larger angle, the detection zone of the IR emitter-receiver section cannot be moved in the depth direction of the door, which results in a large non-detection zone formed between the detection zone of the microwave transmitter-receiver section and the detection zone of the IR emitter-receiver section, where objects can be detected neither by the microwave transmitter-receiver section nor by the IR emitter-receiver section. If a pedestrian stands still in this non-detection zone he or she can be detected neither by the microwave transmitter-receiver section nor by the IR emitter-receiver section. The detection zone of the IR emitter-receiver section may be moved closer to the detection of the microwave transmitter-receiver section by appropriately modifying the installation of the IR emitter-receiver section. In such case, however, a pedestrian standing still in the vicinity of the door cannot be detected, and, therefore, an additional sensor may have to be used to detect pedestrians present close to the door.
IR light, which is used in composite door sensors of the above-described type is subject to influence of external disturbances, such as rain and snow. In other words, IR light can be reflected by raindrops and snowflakes as well as human bodies. Accordingly, a conventional composite door sensor using IR light may detect raindrops or snowflakes as if they were a human body, and may cause a door to open although no object is present in the vicinity of the door.
Therefore, an object of the present invention is to provide a composite sensor with a gap between a detection zone of a radio-wave sensor and a detection zone of an optical sensor which can be made small. Another object of the present invention is to provide a composite sensor for automatic doors with reduced occurrences of erroneous operation of the door which could be caused by external disturbances, such as rain and snow.